Asymmetric Mach-Zehnder Interferometer Based Biosensors for Aflatoxin M1 Detection

Abstract

In this work, we present a study of Aflatoxin M1 detection by photonic biosensors based on Si₃N₄ Asymmetric Mach-Zehnder Interferometer (aMZI) functionalized with antibodies fragments (Fab'). We measured a best volumetric sensitivity of 10⁴ rad/RIU, leading to a Limit of Detection below 5 × 10(-7) RIU. On sensors functionalized with Fab', we performed specific and non-specific sensing measurements at various toxin concentrations. Reproducibility of the measurements and re-usability of the sensor were also investigated.

Keywords: Aflatoxin M1; Fab′; Mach–Zehnder interferometer; biosensor; limit of detection.

Figure 1

Sketch of the asymmetric Mach–Zehnder interferometer chips measured; (inset) photograph of the chip and a one euro-cent coin for comparison. The sensor here is an eight aMZI sensor.

Figure 2

(a) Chemiluminescence detection of AFM1-HRP incubated on Fab′ prepared surface. The protocol described in Section 2.2 was applied changing the Fab′ concentration (incubation time 2 min). (b) For a 0.33 μM Fab′ concentration, the AFM1-HRP recognition was evaluated as a function of the delay before PEG addition (incubation time). The reported values represent the mean value on two different experiments, and error bars are reported as the standard deviation. Exposition times are equal to 0.2 s and 1 s for (a) and (b), respectively.

Figure 3

Volume sensitivity measurements. Evaluation of the bulk sensitivity; (inset) phase shift curve for one of the aMZI sensors during the injection of the water-glucose solutions (glucose concentration in %w/w labelled on the plot).

Figure 4

(a) Sensorgram recorded on aMZI sensors by flowing AFM1 (black) and Ochratoxin (red) through the microfluidic chamber. At t = 0, MES buffer is flowing through the sensors. The toxin was then injected at t = 2.5 min and at t = 25 min. The toxin flow is stopped and the MES buffer was injected again; (b) Sensorgram recorded on one aMZI sensor by flowing a 50 nM (black) and 10 nM (red) AFM1 solutions in the microfluidic chamber. The phase shift is proportional to the Aflatoxin M1 concentration. The actual phase shift is different from the one in (a) since a different sensor was used.

Figure 5

Sensorgram recorded on one single aMZI sensor by flowing a 100 nM AFM1 solution in the microfluidic chamber. The first curve is the response of the fresh sensor, (black line), the second one after one glycine –methanol injection (red line) and the third one after two injections (blue line).

Figure 6

Chemiluminescence detection of AFM1 on Si₃N₄ substrates after regeneration cycles with 100 mM glycine-methanol solution. The data are reported as a mean value of three samples and the error bars are reported as standard deviations.